PARTIAL TRISOMY 16 INTHE MOUSE AS AN ANIMAL MODEL OF DOWN SYNDROME I have recently directed effort toward the development of an animal model of human trisomy 21 (Down syndrome), which could be used to study the mechanisms by which trisomy 21 results in mental retardation, congenital heart disease, and increased incidence of leukemia and infection. To this end, I have mapped three genes, IFRC, SOD-1, and PRGS, which are assigned to chromosome 21 in man, to chromosome 16 in the mouse. These results demonstrate homology between human chromosome 21 and mouse chromosome 16, and suggest that mice trisomic for the homologous portion of chromosome 16 may provide and animal model of Down syndrome. However, more detailed information concerning the degree of homology between mouse chromosome 16 and human chromosome 21 is required to validate the model. Furthermore, the precise segment of chromosome 16 which is homologous to chromosome 21 remains to be determined. Therefore, to obtain this information, I shall use somatic cell genetic techniques to determine the regional chromosomal location and the relative order, in both man and mouse, of five genes which have been assigned to human chromosome 21. This work will provide the basis for constructing mice with partial trisomy 16 as an animal model of Down syndrome.